1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, and more particularly, to a method of forming an isolation film in a semiconductor device by which porous silicon is formed at a portion to be insulated using electrochemical etch and porous silicon is then oxidized, using a thermal oxidation process, to form an isolation film.
2. Background of the Related Art
The semiconductor memory device usually employs a shallow trench isolation (hereinafter called ‘STI’) process as an isolation process. As the cell size is reduced due to higher integration of the semiconductor memory device, the active region and the isolation region are defined using a shallow trench isolation film.
A process of forming the shallow trench isolation film will be now described. A pad oxide film and a pad nitride film are formed on a semiconductor substrate. A photoresist pattern defining an isolation region is then formed. Next, the pad nitride film, the pad oxide film and the semiconductor substrate are etched using the photoresist pattern as an etch mask, thereby forming a trench within the semiconductor substrate.
A high density plasma (HDP) oxide film is deposited to bury the trench. At this time, the HDP oxide film is deposited in a thickness sufficient to deposit the top surface of the pad nitride film while burying the trench. Thereafter, the HDP oxide film is polished by a chemical mechanical polishing (CMP) process. The CMP process is implemented until the pad nitride film is exposed. The pad nitride film is removed. Next, an ion implantation process is performed in order to form a well junction and control the threshold voltage. The pad oxide film is then removed.
However, the above method has disadvantages that the etch process for forming the trench using plasma is difficult due to shrinkage of the trench distance, over-hang occurs at the entrance portion of the trench when the HDP oxide film is gap-filled, seam or void occurs within the trench accordingly, and reliability of the semiconductor device may be degraded since void occurs within the HDP oxide film gap-filling the trench.